The planar extended shape of the phthalocyanine macrocycle results in a strong tendency of its derivatives to form densely packed co-facial aggregates. The strategy to avoid co-facial self-association that forms the basis of this thesis involves the use of substituents that can introduce severe steric crowding adjacent to the phthalocyanine core. Previous work showed that the introduction of 2,6-di-/jo-propylphenoxy groups on the peripheral positions of the phthalocyanine seems to be perfect for this purpose. Of particular interest is zinc octa(2,6-di-/$o-propylphenoxy) phthalocyanine (PclZn), which forms a remarkable cubic crystal structure, containing interconnected solvent-filled voids 2 nm across. The aim of the research programme was to investigate the crystal forming properties of related phthalocyanine derivatives containing different metal cations and bulky phenoxyl substituents. A range of metal cations were introduced into 2,3,9,10,16,17,23,24-octa(2',6'-di-/s0-propylphenoxy) phthalocyanine (Pel) to establish which, if any, were compatible with the formation of the nanoporous cubic crystal observed for the zinc derivative. It was found that any metal capable of binding to a ligand at its axial site formed the cubic crystal including metals of primary catalytic relevance such as cobalt, iron, manganese and ruthenium. Single crystal X-ray diffraction studies demonstrated the exchange of axial ligands to confirm the interconnectivity of the nanovoids, which is essential for the potential exploitation of these molecules in heterogeneous catalysis. Of particular interest is the introduction of bidentate ligands, which act as structural wall ties that bind metals between cubic subunits. Since loss of crystallinity occurs after removal of the guest solvent from the cubic clathrates, the introduction of substituents at the 4-position of the phenoxy groups was also investigated in order to induce stronger dipole-dipole (e.g., R = Br, CI, CN, OMe) or hydrogen bond interactions (e.g., R = OH), which might stabilise the crystal structure. Unfortunately, these derivatives formed non-cubic crystals, although in each case solvent was included within the structure to form novel clathrates.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:584557 |
| Date | January 2009 |
| Creators | Bezzu, Caterina Gavina Grazia |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/54793/ |
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